1. Field of the Invention:
The present invention relates to a high performance solid catalyst component for olefin polymerization catalysts. More particularly, the present invention relates to a new type solid catalyst component capable of exhibiting, when applied to the polymerization of olefins, a high polymerization activity combined with a high stereospecific performance, especially a surprisingly enhanced polymerization activity per titanium atom contained therein.
2. Description of the Prior Art:
From the past, various kinds of olefin polymerization catalysts have been known and widely utilized which are derived from a solid catalyst component comprising a titanium halide and an organoaluminum compound and possess a high catalytic activity. According to these olefin polymerization catalysts, however, the yield of olefin polymers per catalyst component or per titanium atom contained therein does not reach a satisfactorily high level. Thus, a number of studies have been made hitherto for increasing the yield of olefin polymers per catalyst component. In case the yield of olefin polymers per titanium atom is low, the titanium component remaining in the resultant polymers having a strong corrosive action not only causes serious damage of the polymerization apparatus or various devices used in the after-treatment but also gives bad influence on the resultant polymer itself, such as deterioration of its quality or yellowing of the polymer. Hence, there was a strong demand in this art to solve such problems. Although studies have been made to solve the problems by minimizing the titanium content in the catalyst component or by increasing the yield of polymers per unit weight of the catalyst component, a satisfactory result has not yet been obtained for both of the above means. In the majority of cases, a deashing step was needed in the prior arts to eliminate the residual titanium component. As the deashing step requires a large amount of an alcohol or a chelating agent, facilities for recovering or regenerating the alcohol or chelating agent are necessary, thus creating many incidental problems in aspects of resource, energy and the like factors. These were important problems to be solved in carrying out the process for polymerization of olefins in a commercial scale. In recent years, a variety of proposals have been presented to overcome the above mentioned problems. In general, the yield of olefin polymers will be decreased if the titanium content in the catalyst component is suppressed. On the other hand, the titanium content in the catalyst component will become higher if an increased yield of olefin polymer per unit weight of the catalyst component is desired. Thus, it is the current status that any of the proposals cannot overcome the problem that the yield of olefin polymers per titanium atom is low.
In Japanese Patent Publn. No. Sho. 56-52041, for example, there is proposed that a magnesium halide is contacted with an anhydrous compound of an element belonging to Group I, II, III or IV of the Periodic Table to decrease the titanium content in the catalyst component thereby enhancing the activity per titanium. In this prior art, however, the polymerization activity per catalyst component is extremely low, and as the result, the polymerization activity per titanium cannot be said to be satisfactory. In Japanese Patent Kokai No. 62-158704 previously proposed by a part of the present inventors wherein a catalyst component is prepared by bringing a product obtained by suspending a dialkoxymagnesium such as diethoxymagnesium in an aromatic hydrocarbon and contacting the suspension with a titanium halide into further contact with a titanium halide in such manner that a diester of an aromatic dicarboxylic acid is allowed to coexist at any step in the procedure, the polymerization activity per catalyst component can remarkably be enhanced. As the titanium content in the catalyst component is higher in this case, however, the polymerization activity per titanium atom fails to show a fully satisfactory value.
As the amount of an expensive organoaluminum compound used at the time of polymerization is defined in many cases by an Al/Ti molar ratio, a higher titanium content in the catalyst component substantially means the use of a large amount of the organoaluminum compound, thus causing an increase in a unit price of the catalyst in terms of a total catalyst including the organoaluminum compound even if the catalytic activity shows a high value of a certain degree.
Under the circumstances, there is a great demand in this art to develop a new type solid catalyst component which overcomes the problems seen in the prior art catalyst components and can increase the yield of stereospecific olefin polymers per catalyst component.